1. Field of the Invention
The present invention relates to vehicle windshield defrosters and wipers using heated washer fluid.
2. Description of Related Art
Defrosting and deicing of motor vehicle windshields and wipers have been served by conventional warm air defrosters for many decades. There continues to be much driver dissatisfaction with the slow and otherwise poor performance of these defrosters for providing quick and safe driving visibility. Government mandated vehicle safety standards (e.g. FMVSS103 based on 1960s warm air automotive defroster minimal technology) set minimum defrosting performance requirements, yet still allow 30 minutes from cold engine start to clear a preset standard amount of frost at 0° F. Even modern (27.5 miles per gallon CAFE—Corporate Average Fuel Economy) vehicles still typically take 15-25 minutes to defrost the windshield on this test.
Consequently, in commonplace operation drivers often have to scrape ice from the windshield and knock ice off wiper blades or waste fuel and time waiting for the engine to warm up so the defrosters can work. Windshields are especially difficult to access effectively with ice scrapers, and the situation is exacerbated in the U.S.A. with the coming wave of 78 million elderly “baby boomers” having reduced agility to scrape ice from windshields. Also, evidence indicates global warming may be generating more intense storms including during winter.
Much better defroster performance is deemed necessary by many winter weather drivers, especially in light of better available technology such as electrically heated windshields and the even more effective emerging heated washer systems. Substantially intensifying this need for better defrosting systems is the rapidly emerging class of high fuel efficiency internal combustion engine, hybrid, plug-in hybrid electric, full battery electric and fuel cell electric vehicles to achieve the very challenging newly legislated 35.5 mpg CAFE requirement by 2015, a less oil dependent national economy (witness skyrocketing fuel prices) and more environmentally friendly vehicles.
Because of the high fuel efficiency of these coming new vehicles there is inherently much less “waste heat” energy available to enable traditional engine coolant heat based warm air defrosters and heaters to perform well. Automakers and their suppliers are now actively researching and developing new defroster and heater technologies such as heat storage, heat pumps, electrical heating, viscous friction heaters, coolant turbulence heaters and fuel fired heaters to meet the new needs of these highly fuel efficient vehicles. Present day conventional type vehicles of lesser fuel efficiency and greater “waste heat” will largely become obsolete. The common practice of warming up the engine for extended periods of time to defrost the windshield before driving is contrary to the now common goals of reducing pollution and energy dependence on foreign oil.
Remote start feature has been available on the aftermarket for many years and is recently becoming popular as an original equipment feature to enhance defrosting, heating and air conditioning performance. However anti-idling laws of many states and countries, in the interest of reducing air pollution and improving fuel economy, increasingly limit allowable idle time (now typically down to 5 minutes) and the remote start feature will tend to have corresponding idle time restrictions.
Electrically heated windshields can substantially reduce defrost time but have had limited use because of cost, complexity, poor reliability, and technical problems such as interference with electronic communications devices. Electric heated windshield replacement cost is many times more (examples of 5 times more have been discovered) than a conventional windshield and replacement data indicate the average vehicle has about 1½ windshields during its lifetime. Visible heating wires and heating films can also be distracting and degrade windshield clarity and transparency.
Electrically heated washer fluid systems spraying through conventional nozzles have had limited success in the aftermarket but have recently emerged on the original equipment market to augment windshield and wiper deicing performance of warm air defroster systems. Electrical overheating failure has resulted in at least one major product recall. One of the world's largest automakers has recently offered a heated washer system feature available on numerous models, and other automakers have also been planning to offer this feature. Still, even these systems exhibit poor performance, functionality and reliability in the opinion of many users. Although these heated washer systems can reduce the FMVSS103 defrost time from typically 15-25 minutes down to 5-10 minutes, drivers still desire much faster defrosting. Also, when driving in winter icing and blizzard conditions in which visibility becomes poor from iced up wipers and windshield, even with the aid of the warm air defroster on maximum output, available heated washer systems fail to quickly and effectively clear ice and often the driver still has to manually deice the wipers and windshield to achieve safe driving visibility. These heated washer systems commonly do not respond instantly upon driver demand to spray heated washer fluid. Fluid spray is delayed for 30-45 seconds while a small amount of fluid, e.g. 2 ounces, heats up to provide only a 2-3 second spray after which time there is another long delay to heat another small amount of fluid. This process typically takes about 2½ minutes to complete one deice cycle, with repeat cycles often needed. Confusing heated washer driver operated switch controls, along with already and increasingly complex modern instrument panel controls and displays, further add to the complexity and cost of these systems.
Heated washer systems using heat from engine coolant have long been available but also have had little success in the marketplace largely due to slow time to warm up upon engine cold start, low heat transfer rates, issues with washer heater freeze up damage and the heater purging its fluid from boiling of the high vapor pressure alcohol antifreeze laden washer fluid (about 158° F. boiling temperature) in the presence of 200+° F. engine coolant temperatures. Purging not only can waste washer fluid but, more importantly, causes significant delay in spray time from the resulting empty washer fluid heater having to become refilled, and the cold fluid then entering the heater does not have sufficient time to fully heat up as it quickly passes through the heater to get sprayed to the windshield. This limited fluid heat up from quick passage through the heater is largely due the commonly known heat transfer phenomenon of fluid boundary layer thickness (basically defined as the distance of the zero velocity fluid immediately adjacent the flow channel wall to the point at which there is 99% of the maximum flow velocity). In either laminar or turbulent flow, just a modestly thick boundary layer (e.g. 0.10 inches typical of tubular heaters) can prevent very high heat transfer flux in even otherwise well designed heat exchangers. Fortunately, because of relatively low required flow rate and pumping time of the washer fluid pump, and relatively low flow rate requirement of engine coolant (or heat pump fluid or other lower flow rate heating fluid) in the cabin heater circuit, it is possible to construct a very simple compact heat exchanger having an unusually high heat transfer rate. This heater concept, described as the object of this patent application, will have rather high, yet acceptable, flow restriction, with extremely low liquid volume relative to the area of the heat transfer fluid chambers, and with the extremely low liquid volume will therefore be inherently freeze protected because of the small freeze expansion of the small amount of fluid. Its heat transfer flux will be very high by virtue of the forced ultra thin, and therefore extremely low thermal resistance, boundary layers simply by virtue of uniformly and extremely thin flow channel construction, e.g. 0.010 inches (resulting in less than 0.005 inches thick boundary layer), of the washer fluid to be heated flow chamber and engine coolant heating fluid flow chamber. After extensively researching related subject matter this inventor has discovered no prior art of washer fluid heater or other multi liquid heat exchanger construction to make advantage this concept.
To avoid a contributing cause of windshield cracking automakers are known to limit heated washer fluid temperature contacting the windshield to no more than about 125° F. The concentrated thermal shock from hotter fluid than this coming from fluid concentrating conventional nozzles onto sensitive areas of the windshield, such as a small stone crack, scratch or subtle stress concentration at the windshield mounting edge, can readily propagate a large crack in the glass.
Heated washer fluid spray concentrating, and therefore high windshield thermal shocking, conventional nozzles, even of the wider spraying fluidic and spray fanning types, fail to provide the very high degree of broad and uniform heated fluid distribution needed to bring out the great deicing and bug clearing performance capability of an otherwise well engineered heated washer system. Only well designed heated fluid delivering wiper blades provide “close proximity to glass” fluid delivery and near perfectly uniform broad distribution that maximizes defrosting, deicing and bug cleaning performance, while minimizing washer fluid usage, and prove to be the most effective washing means. This broad and uniform distribution enables much higher temperature (e.g. 150° F.-175° F.) fluid to be safely delivered with minimal thermal shock for improved deicing and cleaning and without risk of windshield cracking or scalding of persons.
Another deficiency of available heated washer systems is that they cause the heated fluid to lose a large part of its heat energy through rapid wind chill evaporative cooling of the contained high vapor pressure alcohol antifreeze as the fluid sprays from the nozzles a foot or two through the cold air before reaching the mid and upper reaches of the windshield. The resulting large amount of midair condensing visible steam on actual tests by this inventor is clear evidence of this energy loss. This sudden cloud of steam can also cause momentary reduction of driver visibility, e.g. while making a left turn in the presence of oncoming traffic on a sunny day. Actual testing of my well designed fluid delivering squeegee wiper blade, as subsequently described herein, demonstrates almost total absence of this evaporative energy loss, with a resulting 50% or greater reduction in windshield deice time and fluid usage as compared with using heated fluid through conventional nozzles.
Often washer systems will be filled with water based fluid having insufficient antifreeze which subsequently freezes solid and causes washer heater permanent damage from ice expansion pressure. Washer heater design features to provide freeze protection typically add cost, and the increased complexity can run counter to increasing reliability.
Another shortcoming of available washer fluid heaters is that their effectiveness is inherently limited because, in between the short electronically programmed heated fluid squirts, the remaining heat of the fluid on the windshield and the now slightly warmed glass is quickly dissipated by evaporation and wind chill during the frequent and long fluid reheating delays between these short squirts. The result is delayed defrosting and even partial windshield refreezing while awaiting subsequent programmed heated short squirts which have to reheat the remaining ice to its melting point. This results in extended defrost times best measured in minutes. However actual testing of proof of concept working models of my invention demonstrates if the total heat energy required to melt and clear the ice is delivered in one relatively quick, continuous and very evenly distributed amount of heated fluid directly from the wiper blade rubber squeegee onto the windshield the time for complete defrosting is dramatically reduced to seconds.
Another deficiency of available washer fluid heaters is that they are prone to building up calcium scale and other mineral deposits from the long term heating of washer fluid continuously stored within the heating chamber. This is the same mechanism that causes heavy lime scale buildup in a teapot simmering water over a long period of time. These deposits can choke fluid passage, cause loss of heat transfer efficiency and break loose and clog washer nozzles.
A new heated washer system is needed which will fulfill the following requirements:    1. Upon washer activation must combine virtually instantaneous fluid delivery and heat up to substantial temperature with thermally efficient fluid delivery means such as a wiper blade squeegee that very uniformly distributes heated fluid externally traversing only a small fraction of an inch distance to be distributed directly onto the windshield ice. Must maintain full wiper blade flexibility in icing conditions for good wiping compliance to the windshield, and deliver the ice melting energy needed within a very short time—best measured in seconds. Must have an effective mass production manufacturing process for the wiper blade squeegee that will produce a fluid orifice/nozzle pattern that results in a nearly perfectly optimized distribution of fluid onto the windshield.    2. Should quickly defrost/deice windshield and wipers upon the driver's activation of the conventional steering column mounted washer switch soon after a cold engine start—typically within 20 seconds, or even automatically as could be activated by a windshield frost sensor.    3. Should quickly deice windshield and wipers—typically within 10 seconds—upon driver demand while driving in severe icing conditions.    4. Must be properly adaptable to highly fuel efficient (e.g. 35.5 mpg CAFÉ) vehicles such as low heat rejection internal combustion engines, plug-in hybrid electric, and totally electric vehicles such as battery and fuel cell operated, and also provide excellent defrosting performance for conventional internal combustion engine vehicles.    5. Should not require additional driver controls to operate compared to a vehicle not equipped with a heated washer system, i.e. should be operable by the existing conventional washer switch.    6. Should be resistant to build up of calcium scale and other mineral deposits within the heater.    7. Should be protected from freeze damage of washer fluid and engine coolant, and have 20 year/200,000 mile corrosion protection to meet expected future automotive durability requirements.    8. Must be price and manufacturing cost competitive with a minimum number of component parts.    9. Must be compact for easy vehicle packaging.